Dry stack....

That is not an appropriate application for flagstone.

Pretty strange; from the photos it looks like a single line of loose stone. What was the purpose or goal for this?

I agree with Babs......doesn't appear to be a wall at all but just a line of loose stone. And I also agree a very poorly executed line :-))

If you wanted the bed edged, flagstone is not the best material for that purpose.....in fact, I'd never consider it for that usage. Rock cobbles would be more suited, can be sited tightly together so they look almost like solid edging (which I dislike) and take up less space. Other alternatives are bricks set on edge or even smaller landscape rocks (1/2 man).

I would go for bricks or concrete pavers which can be set tightly enough against each other and down enough into the soil so that they won't shift. I am assuming by rock cobbles GG48 us referring to squared paving cobblestones as opposed to what is referred to as cobble around here meaning rounded water worn rock such as what is found on Maine beaches.

Belgian blocks, jumbo size.

Flagstone is flat natural paving material, used primarily for surfacing (patios, walkways, stoops and stairs, etc.). It can be used as a dry stacked wall but that is not what you have and you would need to use a lot of it for that purpose. It really doesn't work well for edging as it doesn't exactly produce an 'edge'........or not at that height.

Some other edging material would look and function much better.

Since I live in an area where stone often looks like that, small walls like this are something I see. So to my mind, it doesn't look that bad. However, the small rocks used only as filler should go, and the plants should be placed so they cover a good part of the remaining rock. If the idea is a wall, rather than an edging, the wall should be a
couple of courses high, just so it looks like a wall, instead of an
edging. Then the soil level has to be raised behind it, which may or may
not work.

Locally, the difference between paving stone and wall stone is the thickness. Aside from that, it is potentially exactly the same. Depending on the source of the rock, wall stone may also be more irregular, but a lot of the common stones split very evenly on their own.

Given the chronic lack of location information, all I can say is that I wouldn't think of doing something like this anywhere it snows. A shovel could potentially move that edging. A plow could take down a whole wall.

No, you haven't seen flagstone used. You have seen LEDGESTONE used. It needs a good 1' to look good. Smaller mini-walls are made when people live in a rocky area and have to move stones out of the beds to get space for a shovel. Then it is fieldstone that is used--natural fieldstone. It kinda settles into walls once you get used to stacking it.

You should pay the landscaper for his work. This was your fault, not his. Get bricks or Belgian block and install the vertically with half buried. Search "Belgian block curb" for details--it is the same on garden beds as on curbs and the same with brick as with the stone.

You shouldnt put it on the flat/long ways. That will eventually settle so it is too deep.

Stacked flagstone could be used to build a short mortared/ semi-dry Stacked Wall, depending on level of frost heave in your area. The problem is that the pieces tend to shift forward over time if the base and backfill are not properly installed to reduce frost heave. Even with this short curb, 6” of compacted crushed concrete should be used below with a thin sand setting bed for leveling. Free draining crushed stone should be used behind the curb.

The flagstone as laid out is terrible. If you like the look overall, the landscaper would need to eliminate the small pieces and rotate the larger one so they fit closely together.

However, I agree with previous recommendations. Use thicker stone to create the curb. You can get bluestone fieldstone or a variety of other natural ledgestone/ wallstone products that will give a look similar to what you originally envisioned. You could even use mortared flagstone fit tightly together to create a cap if desired. Regardless of the material used, make sure the base is properly installed, including at least 3" of wall stone buried below grade.

Oh! Then the landscaper is an idiot.

Bluestone is usually used for patios, steps, pavers—not as a wallstone. You are looking at beds that are a foot or higher. But your beds aren’t that high. A drystack wall less than 8” isn’t big enough to look good. You’re still wanting something that doesn’t really exist.

Much of the discussion here is based on semantics and what is referred to as "X" in Ohio could just as easily be referred to as "Y" in Tennessee even though it is the identical product. Local terminology is a reference point as there are no industry naming standards for natural stone. Cast concrete products will have proprietary names.

@Omega is correct when he says to ask for material that is 8" deep (if it's available in your market). Here in northern Illinois that material comes from Wisconsin and any contractor I know and any quarry or distributor I know would refer to it as "cut drywall" or "snap-cut drywall". The lengths are random but the depth is nominally 8". It comes in thicknesses ranging from 2"-3" all the way up to 8".

The next two photos are both "cut drywall". When I ordered the stone for these two projects I simply called the distributor and asked for " X tons of 2"-3" cut drywall". At that point I can be comfortable knowing that I will be getting product that is 2"-3" thick, 8" deep and in random lengths. Coverage on this product is roughly 18 face feet (square feet) per ton.

@Omega is also correct in his first post, saying that you CAN build your short wall out of this material. It still requires compacted stone base like a taller wall. If you look at the top photo and visualize only two course of stone above grade that would be your finished height. From the bottom up you would have 6" of stone base, one course of wall below grade and two courses of wall above grade.

When well-built these walls can last for 40-50 years, even longer without an ounce of mortar.

That being said, base on your original photos the "wall" appears to border a driveway and cut drywall is probably not ideal for your situation.

The recommendations of NHBabs and Gardengal48 are infinitely better for your situation based on the photos you posted. The pic posted by @Gardengal48 would be a much better selection for your application and requires far less skill to install than cut drywall. While not available in all markets Techo-Bloc makes a wide assortment of pre-cast bed edging. One of their products is named Belgik after natural Belgian block edging. See link below for assorted options.

https://www.techo-bloc.com/en/product-category/edges/

@Gardengal48 is also correct when she says flagstone is not normally used for walls, but rather in flatwork. Below are two photos of what we locally call flagstone. The first is a an oversized pathway of flagstone set on a gravel base but with mulch in the joints so it looks less refined based on the woodland setting. Bergenia and Hosta flank this path into the backyard. This path has been in place since 2002 and looks as good today as it did back then.

The second photo is a walkway to the front door and as you can see it is mortared into place and a more polished aesthetic. These are usually done on top of concrete which is "under-poured" in anticipation of the flagstone depth. This is a high-skill flagstone installation.

In the end, the skill of your contractor is going to dictate the success of the installation. NHBabs and Gardengal were being kind describing the current installation as 'strange' and 'poorly executed' as I look back at your photos. Show your contractor some photos of what you want and simply ask, "Can you implement this work?". If they fidget, look down at their feet or start gazing aimlessly at your dogwood then it's time to launch them and hire the next man or woman standing.

Good luck with your project!!